A fluid filter is already known, comprising a filter body provided with a principal connection for admission of a fluid to be filtered and, contained inside said filter body: an enclosure for admission of the fluid to be filtered into which said admission connection opens out; a first filtration assembly comprising filtering elements and a first enclosure for receiving the filtered fluid, separated from the rest of the filter by said filtering elements of said first filtration assembly; a second filtration assembly comprising filtering elements and a second enclosure for receiving the filtered fluid, separated from the rest of the filter by said filtering elements of said second filtration assembly; and a device for periodically cleaning the filtering elements of each of said first and second filtration assemblies comprising at least one enclosure for receiving the residues of cleaning from said filtering elements.
FR-A-2 554 735 discloses such a fluid filter, in which the function of the second filtration assembly is to receive the fluid laden with impurities coming from the periodic cleaning of the filtering elements of the first filtration assembly and to ensure filtration thereof. The filtered fluid issuing from the filtration effected by this second filtration assembly presents, in the known filter, substantially the same quality of filtration as that issuing from the principal filtration effected by the first filtration assembly, and is re-introduced in the circuit of the purified fluid. With one filter, the user may thus treat both the principal flow to be filtered and also the secondary flow issuing from the periodic cleaning of the filtering elements of the first filtration assembly.
Requirements concerning filtration have developed and it is admitted at the present time to employ, in certain uses, two distinct filters to make the two filtrations mentioned above. On the other hand, there are uses where it would be valuable, in order to be able to supply %he same machine with purified fluid, to have available a fluid presenting two qualities of purification, if possible by means of the same filter. For example, certain internal combustion engines, of the "Diesel" type, provided with a turbocharger, present double lubrication circuits, for lubrifying, on the one hand, the engine itself, on the other hand, its turbo-compressor. The qualities of filtration are different, the engine admitting a screening of 35 microns, whilst the turbo-compressor requires a screening at the most equal to 20 microns, for example.
By adapting the known filters, it becomes possible, with one sole filter, to obtain the desired flows of filtered fluid, with the desired qualities of filtration.